The present invention generally relates to ink printing technology, and more particularly to a specialized ink containment vessel for use in an ink delivery system which is resistant to the corrosive effects of ink, prevents air entry into the ink, avoids the evaporation of volatile ink components therefrom, and is dimensionally stable during production and thereafter. As a result, the overall longevity and operational efficiency of the entire ink delivery system is improved.
Substantial developments have been made in the field of electronic printing technology. A wide variety of highly-efficient printing systems currently exist which are capable of dispensing ink in a rapid and accurate manner. Thermal inkjet systems are especially important in this regard. Printing units using thermal inkjet technology basically involve an apparatus which includes at least one ink reservoir chamber in fluid communication with a substrate (preferably made of silicon) having a plurality of thin-film heating resistors thereon. The substrate and resistors are maintained within a structure which is conventionally characterized as a "printhead". Selective activation of the resistors causes thermal excitation of the ink materials stored inside the reservoir chamber and expulsion thereof from the printhead. Representative thermal inkjet systems are discussed in U.S. Pat. No. 4,500,895 to Buck et al.; U.S. Pat. No. 4,794,409 to Cowger et al.; U.S. Pat. No. 4,509,062 to Low et al.; U.S. Pat. No. 4,929,969 to Morris; U.S. Pat. No. 4,771,295 to Baker et al.; U.S. Pat. No. 5,278,584 to Keefe et al.; and the Hewlett-Packard Journal, Vol. 39, No. 4 (August 1988), all of which are incorporated herein by reference.
The ink delivery systems described above (and other printing units using different ink ejection devices) typically include an ink containment unit (e.g. a housing, vessel, or tank) having a self-contained supply of ink therein in order to form an ink cartridge. In a standard ink cartridge, the ink containment unit is directly attached to the remaining components of the cartridge to produce an integral and unitary structure wherein the ink supply is considered to be "on-board". However, in other cases, the ink containment unit will be provided at a remote location within the printer, with the containment unit being operatively connected to and in fluid communication with the printhead using one or more ink transfer conduits. These particular systems are conventionally known as "off-axis" printing units. Representative, non-limiting "off-axis" ink delivery systems are discussed in co-owned U.S. patent application Ser. No. 08/869,446 (filed on Jun. 5, 1997 and now U.S. Pat. No. 6,158,953) entitled "AN INK CONTAINMENT SYSTEM INCLUDING A PLURAL-WALLED BAG FORMED OF INNER AND OUTER FILM LAYERS" (Olsen et al.) and co-owned U.S. patent application Ser. No. 08/873,612 (filed Jun. 11, 1997and now U.S. Pat. No. 5,975,686) entitled "REGULATOR FOR A FREE-INK INKJET PEN" (Hauck et al.) which are all incorporated herein by reference. The present invention shall be applicable to both of these designs, and may likewise be used in connection with ink printing devices that employ non-thermal-inkjet technology. Accordingly, while the claimed invention shall be described herein with primary reference to thermal inkjet printing systems, it is likewise applicable to any ink delivery apparatus which employs a housing, vessel, or tank containing a supply of ink therein which has corrosive capabilities and volatile ink components.
An important consideration in the development of an ink containment unit for use with a thermal inkjet (or other type) of printing system is the ability of the containment unit to avoid substantial air introduction into the ink supply and printhead. Excessive air introduction (when reaching a critical volume) can cause a loss of system back-pressure which will typically result in operational failure of the ink ejection components and reduce overall printhead life. It is also important to prevent the evaporation of volatile components from the ink supply, with these components including water and organic solvents such as 2-pyrrolidone; 1,5-pentanediol; N-methyl pyrrolidone; 2-propanol; 2-ethyl-2-hydroxymethyl-1,3-propanediol; cyclohexanol, and others as discussed in considerable detail below. Solvent evaporation can result in a chemical deterioration of the ink supply which will reduce overall print quality and can cause premature failure of the ink delivery printhead. Accordingly, these factors must be carefully considered in any ink delivery system regardless of whether the ink containment unit (e.g. housing, vessel, or tank) is of the "on-board" variety or remotely positioned from the printhead.
Many ink cartridge units have employed rigid, thick-walled ink storage housings for containing ink therein which is present in "free flowing", unconstrained form or held within a multi-cellular foam-type member. Representative ink cartridge units which employ these types of rigid ink containment systems are illustrated in U.S. Pat. Nos. 5,185,614 and 5,168,285. Plastic is commonly used to construct the housings associated with these and other cartridge units. Representative plastic compositions which have been employed in the past for this purpose include but are not limited to polytetrafluoroethylene (Teflon.RTM.), polystyrene plastic, polyethylene terephthalate, polysulfones, and polycarbonate compositions. While these materials typically have good physical strength characteristics, they may be subject to chemical deterioration, undesired fluid permeability problems, gas transfer into and out of the ink supply, and other related conditions depending on the particular ink composition being delivered. Should any of these difficulties actually occur, they will cause operational problems in the printing system of interest (including increased "down-time", enhanced maintenance requirements, ink deterioration, and the like) as discussed above. Likewise, numerous materials are employed in traditional ink formulations which can be characterized as "corrosive" when placed in contact with plastic products (including those listed above). This "corrosion" (or, more specifically, chemical deterioration) is typically caused by the various organic solvents in the ink products which can create the problems outlined herein.
A substantial need has therefore existed for an ink containment unit applicable to both of the systems listed above (namely, self-contained and "off-axis" units) which is durable, impact-resistant, and able to (1) provide appropriate protection against ink corrosion problems; (2) present air from entering the ink supply; and (3) avoid the evaporation of volatile ink components including organic solvents and water from the ink. The present invention described below solves these problems in a unique and highly effective manner. Specifically, a novel ink containment unit (typically in the form of a housing, vessel, or tank) and ink containment method are provided which offer a solution to the problems outlined above including those involving the corrosive effects of ink materials. Furthermore, the compositions and materials discussed below which are used to produce the claimed ink containment vessels provide a considerable degree of thermal and dimensional stability during production and thereafter. In accordance with these benefits, high levels of operating efficiency, excellent print quality, and increased longevity are maintained in connection with the ink delivery systems under consideration. These and other benefits associated with the claimed invention (as well as the specific details thereof) shall be discussed in substantial detail below.